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In recent years, low impact development (LID) has been deemed as an effective strategy for better storm water management. Among tremendous literature concerning the effectiveness of LID facilities to improve urban drainage system (UDS) performance, the scale, location, variety, and parameters of LIDs are fully discussed while the role of urban drainage network is rarely considered. Since LIDs and drainage network work together to realize the function of UDS, this research aims to explore their synergistic effects on the social, environmental, and technological performance of UDS. To represent different synergistic effects, a case area in Kunming, China is divided into upstream, midstream, and downstream sections. The hydraulic and topological characteristics of the drainage network in different sections are varied and 4 LID siting strategies are designed to distribute LID facilities in one of the 3 sections or in the total catchment evenly. Uncertainties from rainfall intensity and LID distribution are discussed as well. Based on the modeling results, the existence of synergistic effect is confirmed. Different spatial relationships between LIDs and the drainage network lead to disparate UDS performance. The synergistic effect may appear as the aggravation or mitigation of the conflicts among various functions of UDS, such as the reduction of urban flooding, combined sewer overflow, and shock loadings to wastewater treatment plant. The synergistic effect is sensitive to the rainfall intensity, suggesting the necessity of system performance investigation under non-design conditions. Due to the complicated synergistic effect, even distribution of LIDs in the target area can be a regretless and simplified solution. The discoveries reveal the significance of the synergistic effect and its implications for the LID planning.